Characterization of Langmuir-Blodgett films of parent polyaniline (original) (raw)
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Composite Langmuir–Blodgett (LB) films of polyaniline and cadmium stearate
Supramolecular Science, 1998
Composite monolayers of cadmium stearate and polyaniline processed with camphor sulphonic acid have been obtained at the air-water interface and subsequently transferred onto substrates as uniform Langmuir-Blodgett multilayers. Pressure-area (-A) isotherm studies indicated that polyaniline molecules are not squeezed out of the cadmium stearate matrix during compression or in the compressed state. Monolayer stability is seen to decrease when the polymer content is increased beyond 60% (in weight) which is probably associated with the formation of microaggregates that also affected the monolayer surface potential at large areas per molecule. With increasing amount of polyaniline in the mixture, a transition from Y-type to Z-type deposition has been observed. Transferred multilayer LB films were characterized by UV-vis, FTIR, XRD, surface potential, and dc electrical conductivity measurements. UV-vis results indicated that though the polyaniline was in the doped state in the spreading solution, the transferred films were in the emeraldine base state. FTIR studies revealed that the transferred films mainly contained cadmium stearate salt in addition to polyaniline. XRD results indicated that the stacking order is dependent on the polyaniline content in the composite films, the order was found to decrease upon increasing the polymer amount. The uniformity of transferred films was confirmed by surface potential studies. A possible packing arrangement in these composite Langmuir and Langmuir-Blodgett films has been proposed. 1998 Elsevier Science Limited.
Comparative studies on Langmuir–Schaefer films of polyanilines
Synthetic Metals, 1999
Langmuir isotherms of polyaniline PANI , poly o-toluidine POT , poly o-anisidine POAS and poly o-ethoxy aniline PEOA were investigated at aqueous subphase of pH 1, where doping during monolayer formation appeared as an essential step for high quality of the film. The effect of substituent groups in polyanilines plays a prominent role for the formation of Langmuir films. The area per unit repeat molecule was shown to increase by an increment of the substituent groups in polyanilines. Ultra-thin films of PANI, POT, POAS Ž . and PEOA were engineered by Langmuir-Schaefer LS technique. The uniformity of the deposited polyanilines LS films was verified by Ž . atomic force microscopy AFM . The electrochemical properties of polyanilines LS films were investigated by cyclic voltammetry and current transient measurements, and the electrical characteristics were investigated by depositing the films on interdigitated electrodes. The electrochromic switching response time and diffusion coefficient of such LS films were also estimated by electrochemical surveyings. q 1999 Elsevier Science S.A. All rights reserved.
Characterization of 16-mer polyaniline composite Langmuir–Blodgett films
Thin Solid Films, 1998
A detailed structural characterization study is presented for composite Langmuir-Blodgett (LB) films containing varying compositions of the 16-mer polyaniline, processed with camphor sulfonic acid and m-cresol, and cadmium stearate. The mixed monolayer approach was selected as it has been proven to yield the most uniform LB films for conducting polymers. Because film uniformity was indeed excellent as verified by visual inspection and also using surface potential measurements, attempts were made to probe whether molecular level mixing occurred. However, X-ray diffraction (XRD) results have shown clearly that the cadmium stearate and the 16-mer molecules are phase separated. Diffractograms were obtained which are very close to that of pure cadmium stearate films, at least for low weight percentages of the 16-mer. When the 16-mer content was increased, the stacking order of the cadmium stearate domains was affected to a large extent, being no longer apparent for 75% of the 16-mer. The presence of cadmium stearate and 16-mer polyaniline in the composite LB film was also detected in a Fourier transform infrared spectroscopy (FTIR) analysis. The deposition of a layer-by-layer structure was confirmed through ellipsometry which also provided film thickness to be compared with the bilayer thickness from XRD data. The thickness was found to be dependent on the film composition, being mostly determined by the cadmium stearate domains up to 50 wt.% of the 16-mer in the composite.
Physical Properties of Polyaniline Films: Assembled by the Layer-by-Layer Technique
Langmuir, 1999
Sequential addition of a polyanion, poly(styrene sulfonate), and a polycation, polyaniline, lead to the formation of layer-by-layer films at different solid surfaces. The prime variables which determine the films formation of poly(styrene sulfonate) (PSS)/polyaniline (PANI) were the polymer charge and ionic strength. The films were deposited by selecting organic/inorganic acid media at pH 2.8. The building up of such multilayer films was characterized by the increment of the adsorbed amount through UV-visible spectroscopy. A linear increase in the absorption magnitude was measured from 1 to 25 bilayers. The uniformity of the PSS/PANI layer-by-layer (LBL) films could be well-maintained, undoping the films in NaOH for obtaining an emeraldine base form of polyaniline. The built-up multilayers were investigated by atomic force microscopy, scanning tunneling microscopy, and cyclic voltammetric and electrical conductivity measurements. The interesting feature of the nearly equal grain size was noticed between 4 and 15 bilayer films of PSS/PANI. The surface roughness was distinguished beyond 15 bilayers of LBL films. The cyclic voltammogram showed the change in the peaks potential value going from 1 to 20 bilayers. The inhomogeneity incorporated inside the films slowed down the electrochemical kinetics in the PSS/ PANI bilayers while going from 1 to 25 bilayer films. The diffusion coefficient (D0) of PSS/PANI 10 bilayers was estimated to be 2 × 10 -8 cm 2 s -1 . Such multilayer films exhibit conductivity in the area of 0.1 S/cm. 10.
Composite Langmuir Monolayers and Langmuir−Blodgett Films from 16-Mer Polyaniline
Langmuir, 1997
The formation of Langmuir monolayers and Langmuir-Blodgett films is reported for the first time for a polyaniline oligomer, 16-mer, that was mixed with cadmium stearate. The processibility of this oligomeric material was greatly improved as compared to the parent polyaniline, which allowed one to use common solvents like chloroform as the spreading solvent. Analogously to composite polyaniline monolayers, the stability and the transferability are found to depend on the 16-mer content in the composite film, with poor stability and low transfer ratios above 60% of 16-mer. Deposited Langmuir-Blodgett films were found to be undoped (or only weakly doped) since they were obtained from monolayers spread onto aqueous subphases (pH) 6.0). Uniform Langmuir-Blodgett (LB) deposition was confirmed by optical microscopy and UV-vis spectra whose intensity increased linearly with the number of layers deposited and also with the 16-mer content. Fourier transform infrared (FTIR) results revealed that cadmium stearate was transferred together with the 16-mer. Upon doping in HCl vapor, the electrical conductivity of the deposited LB films was seen to increase by 1 order of magnitude.
Ultra-thin films of poly (o-ethoxyaniline) formed from doped monolayers
1996
The effect of pH and type of doping acid on monolayer behavior is investigated for poly(o-ethoxyaniline). Doping during monolayer formation is essential for high-quality Langmuir-Blodgett (LB) films to be obtained. Langmuir films were spread on a variety of subphases, containing trifluoroacetic, hydrochloric. sulfuric or perchloric acids at different concentrations. Doping of the polymer occurs at pH values lower than 3 when spreading of the solution is improved. Pressure-area isotherms display less hysteresis and higher collapse pressures when the polymer is pre-doped and spread on a pH = 1 subphase. Under these conditions monolayers could be transferred from the aqueous subphase onto hydrophilic substrates in the form of Z-type LB films.
Preparation and characterization of mixed LB films of polyaniline and cadmium arachidate
Thin Solid Films, 1997
Langmuir isotherms of mixed monolayers of polyaniline and cadmium arachidate have been studied, and rmxed monolayers have been transferred uniformly onto substrates as Langmuir-Blodgett (LB) multilayers. The LB films were characterized by XRD, UV-Vis and FI'IR spectroscopy, dc conductivity and cyclic voltammetric measurements. The FTIR results suggest that the films contain arachidate salt, and the XRD results indicate the presence of a layered structure in the mixed LB films. © 1997 Elsevier Science S.A.
Investigation of fundamental molecular parameters of polyaniline films
Journal of Polymer Science Part B: …, 1999
The effects of fabrication process and solvent on the structure of polyaniline (PANI) emeraldine base films and their intrinsic properties are examined. Freestanding films of PANI base fabricated from N,NЈ-dimethyl propylene urea (DMPU) and N-methyl-2-pyrrolidone (NMP) solutions, by casting and spin-coating procedures and subsequently drawn to different draw ratios, are examined. X-ray diffraction studies show that the PANI films processed from DMPU solution have a noncrystalline structure, whereas the PANI films cast from NMP solution are partially crystalline. The crystal structure is in conformity with the orthorhombic unit cell (EB-II) reported earlier. However, the c parameter of the unit cell was found to be slightly lower than the literature values. A near-infrared waveguide technique was used to determine the three-dimensional refractive indices of the processed and drawn PANI films. The anisotropies developed by the different fabrication and deformation procedures were compared and found to differ. Coupling birefringence and quantitative infrared dichroism measurements yields the intrinsic birefringence and transition moment angles of the infrared absorption bands of PANI.
AFM studies of composite 16-mer polyaniline Langmuir-Blodgett (LB) Films
Synthetic Metals, 1999
Atomic force microscopy (AFM) images of composite Langmuir-Blodgett (LB) ftis containing different weight percentages of cadmium stearate and 16-mer polyaniline are investigated. Upon increasing the amount of 16-mer polyaniline content in the composite, large globular structures x&h higher average roughness could be seen.
European Polymer Journal, 2008
Polyaniline (PANI) films in the form of emeraldine salt (ES) doped with aqueous organic sulfonic acids such as camphorsulfonic acid (CSA), p-toluenesulfonic acid (p-TSA) and dodecylbenzenesulfonic acid (DBSA) were studied. The ES films were obtained by treating the PANI in the form of emeraldine base (EB) with the aqueous solution of the acids. The dopant weight fraction (w), which is related to the mass gain during the redoping of EB, was in situ determined using a quartz crystal microbalance (QCM). The behaviour of PANI doping with different acids indicates that the uptake shows a slow diffusion process. The kinetics of the doping reaction is dominated by Fickian diffusion kinetics. The diffusion coefficients (D) of the dopant ions into the PANI chains were determined and were found to vary within the range of (1.6-18) Â 10 À15 cm 2 s À1. Moreover, the effect of water on these doped ES films was studied. The starting point is the fact that PANI-coated the electrode of QCM shows significant frequency shifts on exposure to water. The changes in the frequency as a function of treatment time in water were quantitatively measured. The response of the device suggests that the mass decrease under water exposure is due to dopant ions release. The latter films were dedoped by exposure to ammonia solution to obtain the EB film form. A further decrease in the mass of the films was observed. The percentage of the mass loss due to water exposure is found to be less than w determined during the dedoping process.